The present invention applies to wearbars for boiler tubes and more particularly, to retrofit wearbars and arc shields for welding the same in place.
In such industries as power generation and particularly in large boiler applications, the air and fuel passing across the boiler tubes within the boiler during entrance and combustion through the boiler can cause severe abrasion and wearing of the surface of the boiler tubes resulting in their early failure and need for replacement. One example of such a high wear characteristic is the cyclone boilers.
Cyclone boilers are generally very large boilers which utilize one or more cyclones at the entrance to the boiler. The cyclones are devices into which extremely high velocity air and fuel are passed in a swirling or cyclone manner around boiler tubes. Primary combustion occurs within the cyclone and the hot gases emerging therefrom are passed upwardly through the main chamber of the boiler.
In some applications, the air velocity within the cyclone can reach velocities in the range of 600 miles per hour. This high air velocity together with the fuel, either oil or coal, being carried with the air creates severe abrading action against the faces of the boiler tubes against which the air fuel combination directly impinges.
One manner in which the boiler tubes within the cyclone are protected from the abrading action of the air fuel mixture in existing boilers is by the use of rectangular wearbars secured to the boiler tubes in a position transverse to the direction of flow of the air fuel so as to protect the boiler tube. FIG. 1 of the drawing illustrates the manner in which a plurality of wearbars 10 are secured to the exterior surface 11 of a boiler tube. The wearbars 10 may be of a wear resistant material such as 310 stainless steel.
During the manufacture of the cyclone portion of the boiler, the wearbars 10 are secured to the boiler tubes during fabrication. Different methods of securing the wearbars to the boiler tube sections during fabrication may be utilized including resistance welding or hand welding. Fabrication by these means is relatively simple during the fabrication stage at the factory during which the various boiler tube segments are disassembled. However, once the cyclone portion of the boiler is assembled at the plant site, the maze of boiler tubes does not readily lend to easy access, repair and replacement of the wearbars.
During operation of the boiler, the continued impingement of the air fuel mixture against the wearbars will eventually erode the wearbars to the point that replacement is required. Accordingly, there are periodic shutdowns of the boiler during which the cyclone is entered and the state of the wearbars examined. Due to the different degrees of impingement of the air fuel mixture upon different portions of the wearbars, some of the wearbars may be only slightly worn whereas others may be excessively worn or even totally missing from the boiler tube. In those cases, either repair or replacement is necessary as the case dictates.
Disassembly of those boiler tubes having damaged wearbars is impractical and too costly. Accordingly, the preferred course of action is to repair the damaged wearbars in situ. Heretofore, this has been accomplished by taking similar wearbars and handwelding them to the worn wearbars or, in the case of missing wearbars, handwelding the wearbars to the boiler tube itself. As is illustrated in FIG. 1, a replaced wearbar 13 is shown wherein handwelding by means of electric arc welding or stick welding as it is known is accomplished by means of puddling a welding pool through an opening 14 provided in replacement wearbars as heretofore used. This procedure is time consuming and thus costly.